Electrical discharge lamp



June 23; 1959 ELECTRICAL DISCHARGE LAMP E. H. GERMER 2,892,113

. Filed .May 12, 1958 FIG.4

JNVENTOR. EDMUND H. GERMER KM //-&r

W6 ,J ATTO EYS United States Patent 7 2,892,113 ELECTRICAL DISCHARGE LAMP Edmund H. Germer, Irvington, N.J., assignor to Engelhard Industries, Inc., Newark, N.J., a corporation of New Jersey Application May 12, 1958, Serial No. 734,518 6 Claims. '(Cl. 313-42) The present invention deals with an electrical discharge lamp and more particularly with a seal for high pressure vapor discharge lamps.

It is well known to provide in electricaldischarge devices, such as mercury vapor lamps having a quartz envelope, a lead-in conductor in the form of a foil of tungsten or molybdenum. The use of such conductors in the form of a thin foil permits the production of a vacuum-type seal between the conductor and the quartz of the envelope. Usually the lamps are provided with quartz extensions welded to the envelope and through which the conductors pass and in which they are partly imbedded with the end portions of the conductors exposed at both ends of the quartz extensions, one end portion extending into the lamp envelopeand the other end portion exposed to the ambient atmosphere with input leads electrically connected to the foils.

Under the high temperature operating conditions of the lamps, the foil conductors, especially at and near the joint with the input leads, are subject to oxidation when the lamp is operating in air resulting in early destruction of the foil and failure of the seal.

It is an object of the present invention to provide a means for extending the useful life of vacuum-tight seals for are lamps. It is another object of the present invention to provide a means for inhibiting oxidation of thin foil conductors under high temperature operating conditions of discharge lamps. Other objects and advantages of the invention will become apparent from the description hereinafter following and the drawings forming a part hereof, in which:

Figure 1 illustrates a partly elevational and partly sectional side view of a seal according to the invention,

Figure 2 illustrates a partly elevational and partly sectional side view of a modification of Figure 1,

Figure 3 illustrates a perspective view of one form of an embodiment of the invention, and

Figure 4 illustrates an elevational view and a side view of another modification of the invention.

The invention relates to a means for reducing the deleteriously high temperatures developed by are lamps at the end of the lamps, especially at the location where the lamp seals are exposed to the ambient atmosphere. The temperature reduction is accomplished by means of a radiator particularly positioned and of particular dimensions.

Regarding Figure l, a vitreous light transmissive lamp envelope or tube 1, e.g. of fused quartz, is provided with an elongated extension 2 of similar or identical composition and welded thereto. A strip of molybdenum or tungsten foil 3 is imbedded in the extension 2 with the ends 4 and 5 extending longitudinally outward thereof, the end 5 extending into the lamp envelope and the end 4 exposed to the ambient atmosphere. Preferably, the ends 4 and 5 are folded upon themselves to increase the foil thickness at such ends and to which ends other components, e.g., electrodes or conductors are welded. For example, electrodes not shown, are welded to the end 5 2,892,113 Patented June 23, 1959 and the conductors, such as stranded wire conductors 6 are brazed or welded to the foil end 4. A radiator 7 according to Figure 1, is welded or brazed to the joint 8, which is a brazed or weld joint connecting the foil end 4 and the end of the conductor 6. The radiator 7 is positioned in close spaced relation to the end 9 of the quartz tube or extension 2.

Figure 2 comprises a modification showing the end 4 of the foil strip 3 imbedded in the extension 2 and connected to the conductor 6, e.g. tungsten wire. In the modification, the radiator 7 is positioned in close spaced relation to the end 9 of the extension 2, and Welded onto the conductor 6. While the-end 4 of the strip Sis imbedded in the quartz extension 2, it is subject to oxidation since the conductor 6 to which it is welded does not provide a hermet-ical seal with the quartz. The radiator 7 is closely spaced from the end 9 of the extension 2, as described with respect to Figure 1, and welded to the conductor 6. In Figure l the conductor 6 leads from the joint 8 and is bent to contact the extension 2 to which it is secured by a tie wire 10 to prevent any undue tension on the joint 3.

In Figure 2, a conductor 11 is welded to the radiator 7 and transmits current through the radiator between the conductors 6 and 11 with the conductor 11 being secured to the extension 2 as in Figure 1.

The radiators employed may have various shapes, for example a curve shape as illustrated by Figure 3 or a disc shape as illustrated by Figure 4.

The radiators consist essentially of a thin metal body of foil dimensions e.g. a ribbon or disc foil having a width exceeding about 10 times the thickness thereof.

One of the reasons of failure of seals is cracking of the seals caused by oxidation of the metal conductors. The seals always have a high temperature during lamp operation which leads to early oxidation of the lead-in foil and its overheating and destruction.

The radiator 7 for example, reduces the danger of cracking of the seals by reducing the heat developed at the end of the lamp and the temperature of the sealed joint and the lead-in conductor. This is attained by positioning the radiator in closely spaced proximity from the seals. The radiator has a large surface and radiates substantial heat which cools the conductors. The radiators may be composed of silver, copper or copper plated silver or nickel plated copper. An especially good radiator is in the form of a silver ribbon or disc having a black coating or a rough surface thereon. Other materials, e.g. aluminum, could also be used. The radiator is connected to the current leading conductor as close as possible to the seal. For example, it is con nected at the location of the joint connecting the input lead 6 and the end of the molybdenum foil 4. When there is an absence of a joint immediately externally of the seal, the radiator can be connected as illustrated by Figure 2.

According to the invention the Width of a radiator ribbon may be from about 3 to 6 mm. with a length of about 1 to 2 cm. and a thickness of from about .25 to 1 mm. This radiator can be straight as illustrated by Figures 1 and 2, curved as illustrated in Figure 3, or in the form of a disc as illustrated in Figure 4. Instead of a single radiator, a plurality of such radiators may be employed in any combination providing an increased radiating surface. In the case of the embodiment illustrated by Figure 2 the current through the radiator 7 has very little resistance when, for example, the disc is composed of material such as silver or copper.

While the invention is particularly described with respect to the illustration, various modifications are contemplated within the scope of the attendant claims.

What is claimed is:

1. An electrical discharge tube comprising a vitreous light transmissive envelope, an elongated vitreous member extending outwardly of the envelope, electrical input means passing through the extending member, a heat conductive foil having a width exceeding about ten times the thickness thereof secured to the electrical input means in closely spaced relation to the free end of the extending member and extending outwardly of the electrical input means.

2. An electrical discharge tube according to claim 1, comprising a black coating on a surface of said foil.

3. An electrical discharge tube according to claim 1, wherein said foil curves outwardly of the electrical input means.

4. An electrical discharge tube according to claim 1, wherein the foil is in the form of a ribbon.

References Cited in the tile of this patent UNITED STATES PATENTS 1,827,292 Laube Oct. 13, 1931 2,042,195 Scott May 26, 1936 2,561,866 Isaacs et al. July 24, 1951 2,763,803 Kreift et a1. Sept. 18, 1956 

